When a cochlear implant of a cochlear implant system is initially implanted in a patient, and during follow-up tests and checkups thereafter, it is usually necessary to fit the cochlear implant system to the patient. For example, during a fitting session, a clinician may utilize a fitting system to set various control parameters associated with (e.g., that govern an operation of) the cochlear implant system and/or otherwise configure the cochlear implant system for operation.
One of the control parameters that is often set during a fitting session for a cochlear implant patient is a most comfortable level (“M level”). An M level represents a stimulation current level required to achieve comfortable loudness to the patient. In other words, the M level represents a stimulation current level, which, when applied to a given set of one or more electrodes associated with the M level, produces a sensed perception of sound by the patient that is moderately loud, or comfortably loud, but not so loud that the perceived sound is uncomfortable.
An M level is typically determined by sequentially increasing the stimulation current level for the patient until the patient reports a comfortably loud sound on a subjective loudness scale. Because the M level anchors the patient's mapping function, defines the patient's electrical dynamic range (thereby impacting a host of perceptual attributes, such as loudness, sound-field-thresholds, spectral contrast, etc.), and is often used to derive other control parameters, accurately determining the M level is highly desirable.
It is a common observation that M levels are often under-fit (i.e., set to be lower than what the patient can actually tolerate) during the fitting process. This is at least in part due to the fact that the patient's tolerance of electrical stimulation is strongly influenced by sound exposure. Many cochlear implant patients have not had much, if any, exposure to loud sounds prior to being implanted with a cochlear implant. Hence, these patients may not initially be able to tolerate relatively high M levels, even though their ability to tolerate high M levels may increase over time as they are exposed to more loud sounds.
Unfortunately, however, M levels are only adjusted during fitting sessions (i.e., when the patient visits a clinic). This means that the M levels are held constant in between the fitting sessions, even though the ability of a patient to tolerate different electrical stimulation levels may fluctuate over time as the patient is exposed to different levels of sound.